Light-emitting diodes ("LEDs") and diode lasers are semiconductor light-emitting devices that produce light through radiative recombination of electrons and holes at a p-n junction formed by either bulk semiconductor materials or quantum well structures. Quantum well p-n heterojunctions have been used to achieve improved light-producing efficiency.
LEDs operate based on the spontaneous emission of photons. An optical cavity may be used in a LED to increase the output intensity. Diode lasers, on the other hand, operate based on the stimulated emission of photons and population inversion. In particular, a diode laser requires an optical cavity to provide necessary optical feedback with a net gain equal to or exceeding the total cavity loss to generate laser oscillations.
LEDs and diode lasers may be configured to have a vertical-cavity-surface-emitting configuration in which the optic axis of an optical cavity is essentially perpendicular to the semiconductor layers including the active layer(s). Thus, the light emitted by such devices is substantially perpendicular to the semiconductor layers. Vertical-cavity-surface-emitting lasers ("VCSELs") can be advantageously used in a wide range of applications to replace edge-emitting diode lasers, such as optical data processing and optical data transmission.